1. Technical Field
The present invention relates to a recording medium transport device for transporting a recording medium in a recording device, and a recording device and a liquid ejecting apparatus equipped with the same.
Herein, the liquid ejecting apparatus is not limited to a recording device such as a printer, a copier, a facsimile, or the like in which an ink jet type recording head is used and for performing recording on a recording medium by ejecting ink from the recording head, and is used to include an apparatus which ejects liquid corresponding to the application instead of ink from a liquid ejecting head corresponding to the ink jet type recording head on a medium to be ejected corresponding to the recording medium to adhere the liquid on the medium to be ejected.
As the liquid ejecting head, besides the recording head, there are included a color material ejecting head used for manufacture of a color filter such as a liquid crystal display, an electrode material (conductive paste) ejecting head used for manufacture of an electrode such as an organic EL display or field emission display (FED), a bioorganic material ejecting head used for manufacture of a biochip, a sample ejecting head as a minute pipette, and the like.
2. Related Art
A printer is an example of the recording device or the liquid ejecting apparatus. There is a printer which includes a recording head, transporting means provided at the upstream side of the recording head and for transporting a recording paper as an example of a recording medium or a medium to be ejected at the downstream side, and discharge means provide at the downstream side of the recording head and for discharging a recording paper on which recording is performed. Then, the transporting means is generally equipped with a transport driving roller rotatably driven and a transport driven roller that can be driven to rotate for nipping a recording medium between with the transport driving roller.
Herein, when printing is performed on the printing paper without making a white space, that is, when performing no frame print, the accuracy of paper feeding is reduced when the back end of the recording paper is passed between the transport driving roller and the transport driven roller (nip point). As a result, there is a case in that the recording quality is deteriorated. Consequently, in order to solve such a conventional problem, a printing device has been developed in which paper transporting speed is set to a low speed when the back end of the recording paper is passed through the nip point of the transport driving roller and the transport driven roller (see Patent Document 1)
However, in the printing device described in Patent Document 1, the problem that the paper transport amount is reduced is unavoidable when the back end of the recording paper is passed through the nip point of the transport driving roller and the transport driven roller. FIG. 8 is a side view of the paper transport pathway for illustrating the problem. Reference numeral 30 denotes a transport driving roller, reference numeral 31 denotes a transport driven roller, reference numeral 30a denotes a rotation axis line position of the transport driving roller 30, reference numeral 31a denotes a rotation axis line position of the transport driven roller 31.
Further, reference numeral H denotes a straight line parallel to the paper transport direction when viewed from the paper transport pathway, reference numeral V denotes a straight line perpendicular to the paper transport direction (straight line H), reference numeral R denotes a straight line passing the rotation axis line positions 30a, 31a, and reference numeral α denotes an angle made by the straight line V and the straight line R. Further, in the coordination system of the drawing, the Y direction denotes paper transport direction and the X direction denotes paper width direction. Note that, the “paper transport direction” denotes the direction in which recording paper should be transported and, for example, is the direction parallel to the head surface of a recording head (omitted in the drawing) provided at the downstream side (right direction in the drawing) of the transport driving roller 30.
Accordingly, when the angle α is not zero, the direction of the paper fed by the transport driving roller 30 and the transport driven roller 31 is not precisely in parallel to the paper transport direction. Then, when a paper guide member (not shown) for supporting recording paper from the lower side is provided at the position opposing the recording head, the angle α is set to a predetermined value (not zero) as shown in the drawing in order to prevent the recording paper to float from the paper guide member and to uniform the distance between the recording surface and the recording head.
Herein, even when a predetermined angle α is set as described above, the recording paper is transported to the downstream side by the outer circumference length of the transport driving roller 30 corresponding to the rotation angle of the transport driving roller 30 during the recording paper is nipped by the transport driving roller 30 and the transport driven roller 31 (the paper shown by the reference numeral P1).
However, when the paper back end is passed through the nip point of the transport driving roller 30 and the transport driven roller 31 (the paper shown by the reference numeral P2), the paper back end is pushed out along the outer circumference of the transport driving roller 30 while the posture of the paper back end becomes close to parallel to the paper transport direction. Consequently, the proceed amount of the paper back end in the Y direction becomes the Y direction component corresponding to the rotation angle β of the transport driving roller 30. That is, the paper back end is not transported by the outer circumference length of the transport driving roller 30 corresponding to the rotation angle β of the transport driving roller 30, so that transport loss occurs.
Note that, even when the downstream side of the paper is pulled by a discharge roller not shown provided at the downstream side of the transport driving roller 30, the paper back end is sandwiched and held between the transport driving roller 30 and the transport driven roller 31 when the paper back end is passed through the nip point of the transport driving roller 30 and the transport driven roller 31. Accordingly, the paper transport amount depends on the transport driving roller 30 and the paper transport accuracy is deteriorated as described above.
Then, the deterioration of recording quality caused by the deterioration of the paper transport accuracy (occurrence of transport loss) when the paper back end is passed through the nip point of the transport driving roller 30 and the transport driven roller 31 as described above is not considered in the above described conventional technique. Consequently, it has been impossible to solve the problem.
Note that, in Japanese Patent No. 3142147, a technique for displacing the contact position of a paper push roller on the circumference surface of a paper feed roller. In the technique, the contact area of a recording paper and the paper feed roller can be adjusted and occurrence of skew caused by the paper feed roller can be prevented by increasing the frictional contact force between the paper and the circumference surface of the paper feed roller by increasing the contact area. However, the above described problem of the invention is not described and not suggested.